Infrared Line Research Articles

Unraveling the Structure-Spectrum Relationship of Yeast Phenylalanine Transfer RNA: Insights from Theoretical Modeling of Infrared Spectroscopy.

Yeast phenylalanine tRNA (tRNAphe) is a paradigmatic model in structural biology. In this work, we combine molecular dynamics simulations and spectroscopy modeling to establish a direct link between its structure, conformational dynamics, and infrared (IR) spectra. Employing recently developed vibrational frequency maps and coupling models, we apply a mixed quantum/classical treatment of the line shape theory to simulate the IR spectra of tRNAphe in the 1600-1800 cm-1 region across its folded and unfolded conformations and under varying concentrations of Mg2+ ions. The predicted IR spectra of folded and unfolded tRNAphe are in good agreement with experimental measurements, validating our theoretical framework. We then elucidate how the characteristic L-shaped tertiary structure of the tRNA and its modulation in response to diverse chemical environments give rise to distinct IR absorption peaks and line shapes. These calculations effectively bridge IR spectroscopy experiments and atomistic molecular simulations, unraveling the molecular origins of the observed IR spectra of tRNAphe. This work presents a robust theoretical protocol for modeling the IR spectroscopy of nucleic acids, which will facilitate its application as a sensitive probe for detecting the fluctuating secondary and tertiary structures of these essential biological macromolecules.

Development and validation of a 64-channel ROIC prototype for SWIR line scan sensor applications

This paper introduces the development and validation of a 64-channel readout integrated circuit (ROIC) prototype, specifically engineered for short-wave infrared (SWIR) line scan sensors. The design of the prototype undergoes various evaluation through comprehensive silicon-level testing, ensuring its robust performance across a variety of operational modes. Key features such as capacitive transimpedance amplifier (CTIA) gain control and sensitivity control are examined, demonstrating the prototype's ability to handle different input currents and capacitance values with precision. Fabricated with 0.18-μm CMOS technology, the ROIC is tailored for integration with Indium Gallium Arsenide (InGaAs) pixels, facilitating high-resolution imaging. The prototype consumes 26.55 mW with A 3.3 V power supply. The fabricated chip show that the total random noise (RN) level is 128 μVrms and column fixed pattern noise (FPN) is 0.16 mVrms

A new instrumentation for simultaneous terahertz and mid-infrared spectroscopy in corrosive gaseous mixtures.

The correct interpretation of infrared (IR) observations of planetary atmospheres requires an accurate knowledge of temperature and partial and global pressures. Precise laboratory measurements of absorption intensities and line profiles, in the 200-350K temperature range, are, therefore, critical. However, for gases only existing in complex chemical equilibria, such as nitrous or hypobromous acids, it is not possible to rely on absolute pressure measurements to measure absolute integrated optical absorption cross sections or IR line intensities. To overcome this difficulty, a novel dual-beam terahertz (THz)/mid-IR experimental setup has been developed, relying on the simultaneous use of two instruments. The setup involves a newly constructed temperature-controlled (200-350K) cross-shaped absorption cell made of inert materials. The cell is traversed by the mid-IR beam from a high-resolution Fourier transform spectrometer using along a White-cell optical configuration providing absorption path lengths from 2.8 to 42m and by a THz radiation beam (82.5GHz to 1.1THz), probing simultaneously the same gaseous sample. The THz channel records pure rotational lines of molecules for which the dipole moment was previously measured with high precision using Stark spectroscopy. This allows for a determination of the partial pressure in the gaseous mixture and enables absolute line intensities to be retrieved for the mid-IR range. This new instrument opens a new possibility for the retrieval of spectroscopic parameters for unstable molecules of atmospheric interest. The design and performance of the equipment are presented and illustrated by an example of simultaneous THz and mid-IR measurement on nitrous acid (HONO) equilibrium.

Test Control of Inclusive Physical Education: Assessment Using the Newest Electronics

The purpose of the study was to determine the effectiveness of a device developed based on the latest electronics to control the coordination of movements of the lower limbs of students with disabilities. Materials and methods. 34 students with disabilities were involved in the study. At the time of the experiment, they had functional disorders of the lower limbs as a result of injuries and received a doctor’s permission to participate in the experiment. The research was conducted at the theoretical and empirical levels, using the following methods: analysis, synthesis, systematization, generalization, technical modeling, pedagogical testing, and mathematical statistics. Results. In the research process, a device was used, which was developed as part of the conducted research. The device consists of two rubber mats in which capacitive proximity sensors are placed. The test task involves recording the number of touches of rubber mats in 20 seconds. The information received from the sensors during the student’s performance of the test task, namely the alternate touching of the rubber mat with the big toe, is sent to the microcontroller via an infrared communication line. The development uses a high-performance microcontroller ATMega 328P, which can support a wide range of sensors and generate information about the time and frequency of leg movements. The signals of the student’s toes touching the rubber mats, received by capacitive sensors, are processed by a microcontroller and displayed on a PC through a serial connection and using the Arduino software, which allows reading the received information about the execution of movements. Under the conditions of the pedagogical experiment, we tried to determine the quality of the measurement results. According to the obtained numerical indicators, the numerical values of the test authenticity obtained by the traditional method of fixing the results by a specialist correspond to the value “low”. The results of the validity calculations showed that the correlation between the test measurement results and the evaluation results using the developed device was optimal with a correlation coefficient greater than 0.6. Conclusions. The importance of a high level of development of the coordination of movements of the lower limbs of students with disabilities is determined by the need to develop this quality to ensure the effectiveness of their rehabilitation in the process of inclusive PE. The analysis of the obtained material allows us to state that the practical application of the inclusive PE device developed based on the latest electronics will allow scientifically based optimization of this process to ensure its effectiveness.

Tool-Wear-Estimation System in Milling Using Multi-View CNN Based on Reflected Infrared Images.

A novel method for tool wear estimation in milling using infrared (IR) laser vision and a deep-learning algorithm is proposed and demonstrated. The measurement device employs an IR line laser to irradiate the tool focal point at angles of -7.5°, 0.0°, and +7.5° to the vertical plane, and three cameras are placed at 45° intervals around the tool to collect the reflected IR light at different locations. For the processing materials and methods, a dry processing method was applied to a 100 mm × 100 mm × 40 mm SDK-11 workpiece through end milling and downward cutting using a TH308 insert. This device uses the diffused light reflected off the surface of a rotating tool roughened by flank wear, and a polarization filter is considered. As the measured tool wear images exhibit a low dynamic range of exposure, high dynamic range (HDR) images are obtained using an exposure fusion method. Finally, tool wear is estimated from the images using a multi-view convolutional neural network. As shown in the results of the estimated tool wear, a mean absolute error (MAE) of prediction error calculated was to be 9.5~35.21 μm. The proposed method can improve machining efficiency by reducing the downtime for tool wear measurement and by increasing tool life utilization.

Ames-2021 CO2 Dipole Moment Surface and IR Line Lists: Toward 0.1% Uncertainty for CO2 IR Intensities.

A highly accurate CO2 ab initio dipole moment surface (DMS), Ames-2021, is reported along with 12C16O2 infrared (IR) intensity comparisons approaching a 1-4‰ level of agreement and uncertainty. The Ames-2021 DMS was accurately fitted from CCSD(T) finite-field dipoles computed with the aug-cc-pVXZ (X = T, Q, 5) basis for C atom and the d-aug-cc-pVXZ (X = T, Q, 5) basis for O atoms, and extrapolated to the one particle basis set limit. Fitting σrms is 3.8 × 10-7 au for 4443 geometries below 15 000 cm-1. The corresponding IR intensity, SAmes-2021, are computed using the Ames-2 potential energy surface (PES), which is the best PES available for CO2. Compared to high accuracy IR studies for 2001i-00001 and 3001i-00001 bands, SAmes-2021 matches NIST experiment-based intensities [SNIST-HIT16 or SHIT20] to -1.0 ± 1.3‰, or matches DLR experiment-based intensities [SDLR-HIT16/UCL/Ames] to 1.9 ± 3.7‰. This indicates the systematic deviations and uncertainties have been significantly reduced in SAmes-2021. The SUCL2015 (or SHITRAN2016) have larger deviations (vs SDLR) and uncertainties (vs SDLR, SNIST) which are attributed to the less accurate Ames-1 PES adopted in UCL-296 line list calculation. The SAmes-2021 intensity of 12C16O2 and 13C16O2 is utilized to derive new absolute 13C/12C ratios for Vienna PeeDee Belemnite (VPDB) with uncertainty reduced by 1/3 or 2/3. Further evaluation of SAmes-2021 intensities are carried out on those CO2 bands discussed in the HITRAN2020 update paper. Consistent improvements and better accuracies are found in band-by-band analysis, except for those bands strongly affected by Coriolis couplings, or very weak bands measured with relatively larger experimental uncertainties. The Ames-2021 296 K IR line lists are generated for 13 CO2 isotopologues, with 18 000 cm-1 and S296K > 1 × 10-31 cm/molecule cutoff and then combined with CDSD line positions (except 14C16O2). The Ames-2021 DMS and 296 K IR line lists represent a major improvement over previous CO2 theoretical IR intensity studies, including Ames-2016, UCL-296, and recent UCL DMS 2021 update. A real 1 permille level of agreement and uncertainty will definitely require both more accurate PES and more accurate DMS.

Transmission Infrared Microscopy and Machine Learning Applied to the Forensic Examination of Original Automotive Paint

Alternate least squares (ALS) reconstructions of the infrared (IR) spectra of the individual layers from original automotive paint were analyzed using machine learning methods to improve both the accuracy and speed of a forensic automotive paint examination. Twenty-six original equipment manufacturer (OEM) paints from vehicles sold in North America between 2000 and 2006 served as a test bed to validate the ALS procedure developed in a previous study for the spectral reconstruction of each layer from IR line maps of cross-sectioned OEM paint samples. An examination of the IR spectra from an in-house library (collected with a high-pressure transmission diamond cell) and the ALS reconstructed IR spectra of the same paint samples (obtained at ambient pressure using an IR transmission microscope equipped with a BaF2 cell) showed large peak shifts (approximately 10cm-1) with some vibrational modes in many samples comprising the cohort. These peak shifts are attributed to differences in the residual polarization of the IR beam of the transmission IR microscope and the IR spectrometer used to collect the in-house IR spectral library. To solve the problem of frequency shifts encountered with some vibrational modes, IR spectra from the in-house spectral library and the IR microscope were transformed using a correction algorithm previously developed by our laboratory to simulate ATR spectra collected on an iS-50 FT-IR spectrometer. Applying this correction algorithm to both the ALS reconstructed spectra and in-house IR library spectra, the large peak shifts previously encountered with some vibrational modes were successfully mitigated. Using machine learning methods to identify the manufacturer and the assembly plant of the vehicle from which the OEM paint sample originated, each of the twenty-six cross-sectioned automotive paint samples was correctly classified as to the "make" and model of the vehicle and was also matched to the correct paint sample in the in-house IR spectral library.

Exploring the limits of the Data-Model-Theory synergy: “Hot” MW transitions for rovibrational IR studies

In order to further improve the accuracy of rovibrational IR line lists generated from the “Best Theory + Reliable High-resolution Experiment” (BTRHE) strategy from 0.01 to 0.05 cm−1, or 300–1500 MHz, to ∼10 MHz, we explore the current limits of the Data-Model-Theory synergy by examining the accuracy and consistency of existing data, then propose that “hot” bands in microwave (MW) spectra is the solution we need for future enhancements. The Ames SO2J = 0–20 rovibrational energy levels computed on the semi-empirically refined Ames-2 potential energy surface (PES) are fit to the Effective Hamiltonian (EH) model regularly used in the experimental infrared (IR) analysis for SO2 isotopologues. In the fitted EH(Ames) model, the rotational constants A/B/C and all 5 quartic centrifugal distortion constants display clear, systematic, and consistent patterns along the vibrational state energy or quanta. Such consistent patterns may facilitate the vibrational assignments for MW hot bands and extract more information from high temperature MW spectra. Some EH(Expt) analyses were carried out with the lowest order Coriolis Coupling term, C1. Their constants should not be directly compared with other EH(Expt) and EH(Ames) results. After excluding them, our δ = EH(Ames)- EH(Expt) analyses for 5 isotopologues (626, 636, 646, 628 and 828) indicates some loss of accuracy and consistency starting from vibrational states as low as 2ν2 or 1000 cm−1. Some EH parameters, e.g. δK, may have relative deviations as large as 50–100% and totally lose any recognizable patterns. This simply means that current EH(Expt) models do not have the system-wide consistency we need to further refine the EH(Ames) and Ames rovibrational IR line lists. A large part of such defects are probably inherited from the limited precision of experimental line positions, i.e. 1E-3 ∼ 1E-4 cm−1, or 3–30 MHz. This is confirmed in a series of truncation tests using the Ames data. Although the EH(Ames) consistency may help identify unreliable rovibrational EH(Expt) parameters, and make reliable predictions for minor isotopologues and unobserved vibrational bands, we believe only the highly accurate “hot” MW transitions can provide real enhancements for EH(Expt) accuracy and consistency. “Hot” MW spectra should play a more significant role in the future synergy of Data, Model, and Theory in the field of rovibrational IR studies.

Line positions and intensities in the ν2 fundamental band of sulfuryl fluoride using the C2v top data system

New experimental high-resolution Fourier-Tansform infrared spectra of the infrared active fundamental ν2 band of sulfuryl fluoride SO2F2, have been recorded at a temperature of 193 K and at resolution of 0.00102 cm−1 at the AILES (Advanced Infrared Line Exploited for Spectroscopy) beamline of the SOLEIL (Source Optimisée de Lumière d’Energie intermédiaire du LURE) Synchrotron facility. A detailed analysis has been performed both in line positions and intensities with the C2vTDS (Top Data System) program suite, based on the tensorial formalism developed in Dijon for quasi-spherical top molecules. The effective Hamiltonian was developed up to fourth order. The parameter of the effective dipole moment operator has been determined using the wavefunctions of the effective Hamiltonian operator. 2407 line positions have been measured with global root mean square deviation of about 0.19 × 10−3 cm−1. Using 71 lines intensities, we estimate the uncertainty on calculated line intensities to 10%. To the extent of our knowledge, this is the first time that an absolute intensity analysis has been carried out for sulfuryl fluoride.

Quantitative validation of Ames IR intensity and new line lists for 32/33/34S16O2, 32S18O2 and 16O32S18O

The quality of Ames-296K SO2 Infrared (IR) line list intensities is first validated by quantitative exploration of several dipole moment surfaces (DMSs) and partition sum convergence. The DMSs are computed with several of Dunning's correlation-consistent basis sets and their vibrational dependence are compared to the empirical model derived from Stark effect experiments reported by D. Patel, D. Margolese, and T.R. Dyke [J. Chem. Phys.70, 2740 (1979)]. The effective dipole deviations from the DMS adopted in the Ames IR lists is 0.2–0.4% for vibrational states up to 3ν3. The vibrational dependence of the dipole moment is also in good agreement, except for nν1. Partition sum convergence at 296 K is confirmed by new calculations with rotational quantum number J up to 150 and upper state E’ up to 8000 cm−1. The isotopologue consistency of the Ames IR line lists is superior relative to the regular Effective Hamiltonian (EH) models and Effective Dipole Moment (EDM) models. The ν1 + ν2 and ν2 + ν3 intensity consistency check reveals the recently reported experimental intensities need significant improvement or re-analysis. After the accuracy, convergence, and isotopologue consistency have been confirmed, the theoretical Ames-296K intensities are combined with the experimental line positions or EH models that experimental spectroscopists published after 2009. Three high-resolution IR line sets are reported for the 32/33/34S16O2, 32S18O2 and 16O32S18O isotopologues: (1) the “New Lines Sets” include experimentally measured line positions; (2) the “Expanded Line Sets” include possible transitions among new rovibrational levels assigned in experiments and ground state (GS) levels predicted by reliable EH models; (3) the “Ames + MARVEL Sets” include possible transitions among all those levels reported in a recent MARVEL analysis. [Tóbiás et al, JQSRT 208, 152 (2018)]. Compared to the limited data in High-resolution TRANsmission molecular absorption database (HITRAN), these line sets have significantly improved the data coverage up to 4000 cm−1. Some missing bands can be traced to the unpublished experimental data. The isotopologue consistency of these line sets will help identify the uncertainties and defects in the experimental EH and EDM models. These line sets are good candidates for the next HITRAN update, if line shape parameters are available. The line sets can be downloaded from supplementary files or from the Ames Molecular Spectroscopic Database at http://huang.seti.org.

Star Formation and Molecular Gas in Extremely Metal-poor Galaxies: Insights from the Thermal Balance in the Neutral Gas

AbstractThe apparent lack of cold molecular gas in blue compact dwarf (BCD) galaxies is at variance with their intense star-formation episode. The CO molecule, often used a tracer of H2 through a conversion function, is selectively photodissociated in dust-poor environments and, as a result, a potentially large fraction of H2 is expected to reside in the so-called CO-dark gas, where it could be traced instead by infrared cooling lines [CI], [CII], and [OI]. Although the fraction of CO-dark gas to total molecular gas is in theory expected to be relatively large in metal-poor galaxies, many uncertainties remain due to the difficulty in identifying the main heating mechanism associated to the cooling lines observed in such galaxies.Investigations of the Herschel Dwarf Galaxy Survey (DGS; Madden et al.2013) show that the heating mechanism in the neutral gas of BCDs cannot be dominated by the photoelectric effect on dust grains below some threshold metallicity due to the low abundance of dust and polycyclic aromatic hydrocarbons, implying that other heating mechanisms need to be invoked, along with a new interpretation of the corresponding infrared line diagnostics. In the study presented here and in Lebouteiller et al. (2017), we use optical and infrared lines to constrain the physical conditions in the HII region + HI region of the BCD I Zw 18 (18 Mpc; ≍2% solar metallicity) within a consistent photoionization and photodissociation model. We show that the HI region is entirely heated by a single ultraluminous X-ray source with important consequences on the applicability of [CII] to trace the star-formation rate and to trace the CO-dark gas. We derive stringent upper limits on the size of H2 clumps that may be detected in the future with JWST and IRAM/NOEMA. We also show that the nature of the X-ray source can be inferred from the corresponding signatures in the ISM. Finally we speculate that star formation may be quenched in extremely metal-poor dwarf galaxies due to X-ray photoionization.

Influence of Non-fundamental Modes on Mid-infrared Spectra: Anharmonic DFT Study of Aliphatic Ethers.

Fundamental and non-fundamental vibrational modes, first overtones, and binary combination modes of selected aliphatic ethers (di-n-propylether, di-iso-propylether, n-butylmethyl ether, n-butylethyl ether, di-n-butyl ether, tert-buytlmethyl ether, and tert-amylmethyl ether) were modeled in a fully anharmonic generalized second-order vibrational perturbation theory (GVPT2) approach on the DFT-B2PLYP/SNST level. The modeling procedure of theoretical line shapes took into account conformational isomers of studied molecules. The calculated spectra of the above ethers were compared to the corresponding experimental spectra in the infrared (IR) region (4000-560 cm-1) of the absorption index k(ν) derived from the neat liquid thin-film transmission data. It was found that IR spectra of aliphatic ethers are heavily influenced by the bands originating from non-fundamental modes, particularly from the combination modes in the C-H stretching region (3200-2800 cm-1). Because of the effects of vibrational resonances, the intensities of overtones and combination bands originating from methyl and methylene deformation modes increase sufficiently to influence the experimental line shape in this region. Less significant contributions from non-fundamental vibrational modes were noticed in the lower IR region (1600-560 cm-1), particularly in the vicinity of the C-O stretching band. The 2700-1600 cm-1 region, which is rich in weak bands due to non-fundamental vibrations, was reproduced accurately as well. It was concluded that a fully anharmonic approach allows significantly more accurate reproduction of the complex IR line shapes, particularly in the C-H stretching region of aliphatic ethers. On the basis of the achieved agreement between the experimental and calculated spectra, it may be concluded that the anharmonic GVPT2 method can adequately reproduce the anharmonic effects and vibrational resonances in particular, influencing the IR spectra of aliphatic ethers. The results obtained in this study show that the non-fundamental modes may play a significant role in shaping the IR spectra of aliphatic ethers and similar molecules in the neat liquid phase.

Fully Photonic Wireless Link for Transmission of Synchronization Signals

Rapid industrialization and increasing demand of business tools for high-speed communications supports the request for optical communications in free space. Cop- per cables and related technologies such as cable modems and Digital Subscriber Line (DSL) are common in existing networks, but do not meet the bandwidth requirement in the future, which opens the door to optical wireless communi- cation technologies. Research in links for optical wireless communication (Infra Red Line of Sight, IR LOS) working in the atmosphere is due to the wide support of its develop- ment on the world market. Optical wireless communications research is currently focused on increasing the transmission quality of data links. A promising new trend in data con- nection through IR LOS includes the transfer of accurate time synchronization pulses (time transmission). The article presents problems of modeling and design of a transmitter and receiver with a fully photonic concept. The analysis of the power levels at the link and drawn a model for determin- ing the connection losses at the receiver caused by optical coupling between a Schmidt-Cassegrain telescope and the receiving optical fiber is shown.

Collisional excitation of [C ii], [O i] and CO in massive galaxies

Many massive galaxies at the centres of relaxed galaxy clusters and groups have vast reservoirs of cool (~10,000 K) and cold (~100 K) gas. In many low redshift brightest group and cluster galaxies this gas is lifted into the hot ISM in filamentary structures, which are long lived and are typically not forming stars. Two important questions are how far do these reservoirs cool and if cold gas is abundant what is the cause of the low star formation efficiency? Heating and excitation of the filaments from collisions and mixing of hot particles in the surrounding X-ray gas describes well the optical and near infra-red line ratios observed in the filaments. In this paper we examine the theoretical properties of dense, cold clouds emitting in the far infra-red and submillimeter through the bright lines of [C II]157 \mu m , [O I]63 \mu m and CO, exposed to these energetic ionising particles. While some emission lines may be optically thick we find this is not sufficient to model the emission line ratios. Models where the filaments are supported by thermal pressure support alone also cannot account for the cold gas line ratios but a very modest additional pressure support, either from turbulence or magnetic fields can fit the observed [O I]/[C II] line ratios by decreasing the density of the gas. This may also help stabilise the filaments against collapse leading to the low rates of star formation. Finally we make predictions for the line ratios expected from cold gas under these conditions and present diagnostic diagrams for comparison with further observations. We provide our code as an Appendix.

Electron Localization of Anions Probed by Nitrile Vibrations.

Localization and delocalization of electrons is a key concept in chemistry, and is one of the important factors determining the efficiency of electron transport through organic conjugated molecules, which have potential to act as "molecular wires". This, in turn, substantially influences the efficiencies of organic solar cells and other molecular electronic devices. It is also necessary to understand the electronic energy landscape and the dynamics that govern electron transport capabilities in one-dimensional conjugated chains so that we can better define the design principles for conjugated molecules for their applications. We show that nitrile ν(C≡N) vibrations respond to the degree of electron localization in nitrile-substituted organic anions by utilizing time-resolved infrared detection combined with pulse radiolysis. Measurements of a series of aryl nitrile anions allow us to construct a semiempirical calibration curve between the changes in the ν(C≡N) infrared (IR) shifts and the changes in the electronic charges from the neutral to the anion states in the nitriles; more electron localization in the nitrile anion results in larger IR shifts. Furthermore, the IR line width in anions can report a structural change accompanying changes in the electronic density distribution. Probing the shift of the nitrile ν(C≡N) IR vibrational bands enables us to determine how the electron is localized in anions of nitrile-functionalized oligofluorenes, considered as organic mixed-valence compounds. We estimate the diabatic electron transfer distance, electronic coupling strengths, and energy barriers in these mixed-valence compounds. The analysis reveals a dynamic picture, showing that the electron is moving back and forth within the oligomers with a small activation energy of ≤kBT, likely controlled by the movement of dihedral angles between monomer units. Implications for the electron transport capability in molecular wires are discussed.

A robust obstacle detection method for robotic vacuum cleaners

Conventional robotic vacuum cleaners (RVCs) with ultrasonic or infrared (IR) sensors present problems in detecting obstacles when they clean the floor in complex situations, for example, under tables or chairs with thin legs. This paper presents a robust obstacle detection (OD) method based on the triangulation principle for RVCs operating in various home environments. The proposed method uses the IR emitter of the RVC to project a horizontal IR beam toward the floor, following which the RVC's wide-angle vision camera captures an image that includes the IR line reflected by the floor or an obstacle. Obstacles are detected by using the image coordinates of the pixels that belong to the IR line in the captured image. Accurate separation of the IR line from the image background is accomplished by defining and minimizing an energy function based on the characteristics of the IR line. The proposed method was tested on the embedded RVC system and was shown capable of achieving OD performance compared with existing methods.

Reliable infrared line lists for 13 CO2 isotopologues up to E′=18,000 cm−1 and 1500 K, with line shape parameters

Reliable infrared (IR) line lists are reported for the 13 isotopologues of carbon dioxide in HITRAN notation: 626, 636, 628, 627, 828, 727, 827, 638, 637, 737, 838, 738, and 646. Three IR lists are available for each istotopologue: a complete list at 296K, a reduced-size list at 296K, plus a reduced-size list at 1000K. They are denoted Ames-296K, Ames-296K.reduced and Ames-1000K.reduced. With J up to 150, and energy up to 18,000cm−1 above the zero point energy, these lists are expected to cover the temperature range up to 1500K. Line shape parameters including temperature dependence are calculated and reported for four temperature ranges: Mars, Earth, Venus, and Hotter (700–2000K). Comparisons are made against the available transition data in the HITRAN2012 models. Line position accuracy for most transitions up to 10,000–13,000cm−1 is better than 0.03–0.05cm−1. Computed transition intensities agree well with most HITRAN data but there exist suspicious exceptions for isotopologues. These line lists will expedite CO2 IR experimental data analysis and provide the scientific community with trustworthy alternatives for unknown IR bands. These line lists may be combined with existing experimental databases to facilitate the analysis of future laboratory experiments or astronomical observations.

INTERPRETING NEAR-INFRARED HYDROGEN LINE RATIOS IN T TAURI STARS

In accreting young stars one of the prominent spectral features in the near infrared is the Paschen and Brackett series in emission. We examine hydrogen line ratios for 16 classical T Tauri stars from SpeX spectra and and assess the trends with veiling and accretion. The observed line ratios are compared to two theoretical models for line formation: (1) Baker and Menzel's (1938) Case B for radiative ionization and recombination and (2) a set of local line excitation calculations designed to replicate the conditions in T Tauri winds and magnetic accretion columns (Kwan & Fischer 2011). While the comparison between Case B and observed line ratios implies a wide range in electron density and temperature among the hydrogen line formation regions in T Tauri stars, the predictions of the local line excitation models give consistent results across multiple diagnostics. Under the assumptions of the local line excitation calculations, we find that n_H in the hydrogen line formation region is constrained to 2x10^10 -- 2x10^11 cm^-3, where stars with higher accretion rates have densities at the higher end of this range. Because of uncertainties in extinction, temperature is not well delineated but falls within the range expected for collisional excitation to produce the line photons. We introduce new diagnostics for assessing extinction based on near infrared hydrogen line ratios from the local line excitation calculations.

Semi-empirical 12C16O2 IR line lists for simulations up to 1500 K and 20,000 cm−1

New semi-empirical Infrared (IR) line lists for 12C16O2, Ames-296K and Ames-1000K, have been computed using a newly updated ab initio CCSD(T)/aug-cc-pVQZ dipole moment surface (denoted DMS-N2) and an empirically refined potential energy surface (Ames-1). J=0–150 rovibrational levels are computed up to 30,000cm−1, and related transitions are cut off at 1E−42cmmolecule−1 (296K) and 1E−36cmmolecule−1 (1000K). These are the first line lists available to cover reliably the energy region as high as ~20,000cm−1. Recent experimental data at 1.1μm has confirmed the predicted intensities for the 50013-00001 and 50014-00001 band transitions have better than 90% agreement. Comparisons are made against the Wattson 750K line list and HITEMP/HITRAN at 300K, 500K, 725K, 1000K, 1500K, 2000K and 3000K. The temperature dependence and accuracy of the new Ames-296K/1000K line lists are investigated and we claim both line lists are capable of providing reliable opacities up to 18,000–23,000cm−1, while the highest applicable wavenumber range drops as T rises. We suggest caution is used for T>1000K simulations. Comparison to recent experiments at 1000K, 1550K and 1773K shows that the Ames-1000K line list and HITEMP perform similarly in the 3200–3800cm−1 and 4600–5200cm−1 ranges. In the 2000–2100cm−1 range, Ames-1000K yields better agreement relative to experiment. Existing problems and possible future solutions in the new Ames-296K/1000K line lists for line positions and intensities are also discussed.

High resolution far-infrared Fourier transform spectroscopy of radicals at the AILES beamline of SOLEIL synchrotron facility

Experimental far-infrared (FIR) spectroscopy of transient species (unstable molecules, free radicals, and ions) has been limited so far in both emission and absorption (mainly by the low probability of spontaneous emission in that spectral range and the low brightness of continuum sources used for absorption measurements, respectively). Nevertheless, the FIR spectral range recently became of high astrophysical relevance thanks to several new observational platforms (HERSCHEL, ALMA...) dedicated to the study of this region suitable for the detection of the emission from cold objects of the interstellar medium. In order to complete the experimental dataset concerning transient species, three discharge experiments dedicated to the recording of high resolution FIR spectra of radicals have been developed at the Advanced Infrared Line Exploited for Spectroscopy (AILES) which extracts the bright FIR synchrotron continuum of the synchrotron facility SOLEIL. These experiments make use of a high resolution (R = 0.001 cm(-1)) Bruker IFS125 Fourier transform (FT) spectrometer. An emission setup (allowing to record spectra of radicals excited at high rotational and vibrational temperatures) and two absorption setups (exploiting the bright synchrotron source at the highest resolution available on the FT) are alternatively connected to the FT. The advantages and limitations of these techniques are discussed on the basis of the recent results obtained on OH and CH radicals. These results constitute the first FIR spectra of radicals using synchrotron radiation, and the first FIR spectrum of a C-bearing radical using FT-spectroscopy.